Aerostat intended to travel in an autonomous and reversible manner between the ground of a planet having an atmosphere and a predetermined ceiling altitude

ABSTRACT

The invention relates to an aerostat of the double balloon type intended to travel in an autonomous and reversible manner between the ground of a planet having an atmosphere and a predetermined ceiling altitude. This aerostat is of the type comprising a first closed carrier balloon (1) for containing a gas lighter than the gas present in the atmosphere, and a solar hot air balloon (3) comprising a permanent opening (6) permitting its filling by the gas present in the atmosphere. According to the invention the solar hot air balloon is provided at its upper extremity with an opening defined by an annular border, and means for sealingly securing this annular border to the peripheral wall of the carrier balloon (1), such that said carrier balloon extends partially into the interior of the envelope of the hot air balloon (3).

The invention relates to an aerostat intended to travel in an autonomousand reversible manner between the ground of a planet having anatmosphere and a predetermined ceiling altitude.

One of the near future objectives of space conquest is to send a missionto the planet Mars. For this reason, several techniques have beenproposed in order to explore this planet. Among these techniques, hasbeen envisaged the provision of a space balloon able to travel in anautonomous and reversible manner between the ground of the planet and apredetermined altitude. This solution presents in effect the advantageof permitting simultaneously a study of the ground of the planet and theatmosphere surrounding the planet. Such an objective cannot be achievedby drawing inspiration from the techniques used for providing captiveballoons such as described particularly in U.S. Pat. No. 3,773,279, orthe free balloons described in French Patent 1,535,761, or U.S. Pats.3,484,058 and 4,394,998.

For this reason, the studies carried out have been oriented toward theprovision of a space balloon conceived for conquering the relativeradiation balance between the day and the night, in such a manner as toabsorb the radiation from the altitude during the day and to lose itduring the night.

In this sense, a first solution consisted in providing a space ballooncomprising a closed envelope containing a gas which is lighter than thegas present in the atmosphere, provided with an internal metallized facein order to permit a sufficient reheating of this gas. The mass of gasis further adapted such that the balloon cannot leave the ground duringthe night by reason of the low temperature of the gas, and gain altitudeduring the day upon reheating of this gas. This solution, the greatadvantage of which resides in its simplicity, nevertheless presents afundamental disadvantage. In effect, on the ground, the volume of gasenclosed in the envelope is low, and when the space balloon arrives atits ceiling, the same mass of gas occupies the total of the envelopebecause of the low pressure of the ambient atmosphere. This very hot gascauses great overpressures which can lead to bursting of the spaceballoon. To sustain these overpressures, the only solution is to providean envelope of a very strong material. However, this solution is notadapted to the nature of the mission by reason of the significant weightof such an envelope, incompatible with transportation by satellite.

To overcome this inconvenience, a second solution has consisted incoupling a first balloon, comprising a closed non-metallic envelope bymeans of a connection to a solar hot air balloon having a permanentopening. This solution is described in French Patent 2,360,089 and hasconsisted of combining the effects of a carrier balloon providing aconstant ascending force which is insufficient to permit the assembly togain altitude, and a hot air balloon furnishing a rising force whichvaries as a function of the temperature and the density of the gasavailable in the ambient atmosphere. This hot air balloon thus furnishesa maximum ascending force at low altitudes which diminishes in relationto the elevation of the assembly. The risks of an over pressurecondition of the carrier balloon are therefor diminished. However, thissolution also has disadvantages. In effect the risks of an overpressurecondition of the carrier balloon, while reduced, exist just the same byreason of the ascending force of the hot air balloon which encloses avery hot gas. Moreover, the launching of such a system from the groundis very hazardous, particularly in the case of violent winds. In effect,when the assembly is on the ground, the carrier balloon and the hot airballoon are maintained above the ground due to the lift of the carrierballoon. The hot air balloon is therefor subject to the action of thewind and may be emptied and take the shape of a spinnaker if it is notprovided with an interpolar connection, or extending itself around itsinterpolar connection if, as described in French Patent 2,360,089, it isprovided. In one case or the other, the beginning of its filling will bevery hazardous.

The present invention seeks to overcome the disadvantages of the abovedescribed aerostats and has as its essential object to provide anaerostat capable of travelling in an autonomous and reversible mannerbetween the ground of a planet and a predetermined ceiling altitudewithout risk of an overpressure condition at the ceiling altitude andnot departing from the ground.

Another object is to provide an aerostat of a relatively light weightand having a good ratio of ascending force to mass.

Another object is to provide an aerostat of a conception adapted topermit any type of mission desired.

To this end, the invention relates to an aerostat of the double balloontype comprising:

a first carrier balloon comprising a closed envelope defining an upperpole and a lower pole and intended to contain a gas which is lighterthan the gas present in the ambient atmosphere,

a second, hot air balloon comprising an envelope produced from amaterial able to absorb solar radiation and emit infrared radiation tothe interior of the volume which it defines so as to heat the enclosedgas, said envelope comprising a lower extremity having a permanentopening intended to permit refilling of the hot air balloon by the gaspresent in the ambient atmosphere.

According to the present invention, this aerostat is characterized inthat:

the carrier balloon is formed of an envelope having a symmetry ofrevolution about an axis and produced from a material transparent to thesolar radiation and comprising an essentially cylindrical portion, andan upper pole and a lower pole situated on the axis of revolution,

the solar hot air balloon comprises an envelope having a symmetry ofrevolution about an axis and including an essentially cylindricalportion provided:

with an open extremity opposite its lower extremity and defined by anannular rim of a cross-section conjugate to that of the carrier balloon,

with a flattened bottom including a permanent opening,

sealed fixing means for the securing the annular rim of the hot airballoon to the peripheral wall of the carrier balloon and adapted tosecurely connect the envelopes of the carrier balloon and the hot airballoon so that the carrier balloon extends partially into the interiorof the envelope of the hot air balloon.

The basic idea of the invention it therefor to associate a carrierballoon with a constant mass and variable volume with a solar hot airballoon of a variable mass and volume which has:

a maximum volume on the ground and in the lower layers in order toobtain a maximum effectiveness upon leaving the ground, and in the lowerlayers,

a lower volume at altitude which confers a low effectiveness, almostnil, in order to avoid placing under pressure and bursting of thecarrier balloon.

The process for producing such an aerostat is of the type comprising:

providing a first closed envelope, termed carrier balloon, defining alower pole and a upper pole and intended to enclose a gas lighter thanthe gas present in the atmosphere,

providing by means of a material able to absorb solar radiation andeminent infrared radiation a second envelope, termed the hot airballoon, comprising a lower extremity provided with a permanent opening.

This process is characterized in that it comprises:

estimating the variation in lift per unit of volume, of the hot airballoon in the absence of and in the presence of solar radiation anddetermining the volume of this hot air balloon necessary to obtain thelaunching of the aerostat, and the load carried thereby,

determining a mass of gas ml which, in the absence of solar radiationis:

necessary in the carrier balloon to assure maintaining the carrierballoon and the hot air balloon above the ground,

less than the mass of gas necessary in the carrier balloon to achievelaunching of the aerostat and the load,

providing a carrier balloon comprising an envelope of a materialtransparent to solar radiation and having a symmetry of revolution aboutan axis and comprising an essentially cylindrical portion, and an upperpole and a lower pole situated on the axis of revolution, said carrierballoon being of dimensions adapted such that its volume is essentiallygreater that the volume occupied by the mass of gas ml at thepredetermined ceiling altitude,

providing a hot air balloon having a symmetry of revolution about anaxis and an essentially cylindrical portion having:

an open upper extremity defined by an annular rim of a cross sectionconjugate with that of the carrier balloon,

a flattened bottom comprising a permanent opening, engaging that hot airballoon around the carrier balloon at its annular edge in such a mannerthat:

the carrier balloon extends partially into the interior of said hot airballoon,

the annular edge of the hot air balloon is positioned opposite a zone ofthe cylindrical portion of the carrier balloon urged intocircumferential tension, on the ground, for a mass of gas ml,

the residual volume of the hot air balloon on the ground corresponds tothe volume necessary to obtain the launching of the aerostat and theload,

fastening the annular border of the hot air balloon to the periphery ofthe envelope of the carrier balloon.

The reliability of the operation of this aerostat rests on the followingpoints:

the fastening of the hot air balloon is carried out on a portion of theenvelope of the carrier balloon which is urged into circumferentialtension, on the ground, in such a manner as to confer on the hot airballoon a significant residual volume. The least reheating of the massof gas thus enclosed in the interior of the hot air balloon brings abouta rapid filling thereof. It should be noted, further, that this residualvolume is also the moreso important than the volume of the carrierballoon is less important on the ground, by reason of the significantgas pressure present in the atmosphere,

upon launching, and in the lower layers, the hot air balloon rapidlyacquires its maximum volume and thus furnishes the maximum liftingforce,

in relation to the ascent, the expansion of the mass of gas contained inthe carrier balloon causes differentially the reduction of the volume ofthe hot air balloon and as a result a reduction in the lifting forcethereof,

when the sun is positioned at the zenith, the fact that the hot airballoon does not have a dome causes a reduction in the heating of thegas which it encloses.

These latter two points work together in order that the pressure of thehot air balloon is progressively weaker in relation to the ascent, andthat as a result, the aerostat does not climb as high as the aerostatsdescribed before. The risks of causing an overpressure in the carrierballoon are thus reduced.

It should also be noted that the lift of this aerostat is assured inlarge part by the carrier balloon which guarantees against any risk ofthe balloon falling. The hot air balloon itself permits providing abalance of pressure which permits obtaining fluctuations and as a resulta control in the vertical direction.

Such an aerostat further presents an overall thermo-optical coefficientwhich can be controlled as a function of its elongation and the natureof the materials of the envelopes of the carrier balloon and the solarhot air balloon. Elongation and the nature of the materials constituteparameters which are easily mastered. For this reason, the overallthermal balance of such an aerostat is completely controlled, and itscharacteristics may be adapted to the type of mission desired with theguarantee of a natural launching at the beginning of the day, a rapidascent upon rising of the sun, and a minimum heating of the carrierballoon at the ceiling altitude, suppressing all risk of bursting.

Other characteristics and advantages of the invention will becomeapparent from the detailed description which follows with reference tothe attached drawings which show, by non-limiting example, a preferredembodiment.

In these drawings which form an integral part of the presentdescription;

FIG. 1 is a longitudinal cross-section along a vertical plane of anaerostat according to the invention, located in proximity to the ground,

FIG. 2 is a longitudinal cross-section thereof along a vertical plane inthe lower layers of the atmosphere,

FIG. 3 is a longitudinal cross-section thereof along a vertical plane atits ceiling altitude,

FIG. 4 is a bottom view of the flattened bottom of a hot air balloonaccording to the invention,

FIGS. 5a and 5b illustrate two steps in the production of the flattenedbottom of this hot air balloon.

The aerostat shown in FIGS. 1, 2 and 3 is intended to travel in areversible and autonomous manner between the ground of a planet havingan atmosphere, such as Earth or Mars, and a predetermined ceilingaltitude.

This aerostat comprises first a carrier balloon 1 comprising an envelopehaving a symmetry of revolution about an axis, provided with anessentially cylindrical portion and an upper pole an a lower polesituated on this axis of revolution.

This envelope is made from rectangular gores of a polyester film of 3.5microns thickness, according to the process described in French Patent80.00343 in the name of the present applicant. This envelope comprisesan interpolar connection 2 connecting its upper pole and its lower pole.

The envelope of this carrier balloon 1 encloses a mass of gas ml lighterthan the gas present in the atmosphere. This mass of gas ml iscalculated in such a manner that the carrier balloon 1 has:

a state of being full at a predetermined ceiling altitude greater thanthe ceiling altitude provided in the conditions of exploration in such amanner that the envelope is never placed into overpressure,

a state of minimal inflation on the ground for which:

the upper portion of the envelope is urged into circumferential tension,

it has a sufficient lift to maintain the aerostat above the ground andinsufficient to bring about launching of this aerostat and its load.

The aerostat comprises secondly, a second solar hot air balloon envelope3, having a symmetry of revolution about an axis, comprising anessentially cylindrical portion 4 and a flattened bottom 5 provided witha permanent opening 6.

The cylindrical portion 4 of this envelope has a cross-section conjugatewith that of the envelope of the carrier balloon 1, and it provided withan open extremity defined by an annular rim or border. This cylindricalportion 4 is produced, as before, by assembly of rectangular gores of apolyester film of 3.5 microns thickness. The internal face of thesegores is further coated with a thin metallic film, for example aluminum.

Such an envelope permits reheating of the gas which it encloses. Ineffect, the solar radiation is absorbed by the polyester film whichtransmits the radiation by conduction to the metallic film. This filmre-emits the radiation then in the form of infrared radiation to theinterior of the envelope.

This cylindrical portion 4 is threaded around the carrier balloon 1 byits annular edge in such a manner as to extend partially into theextension of the lower pole of the latter. It is then fixed in a sealingmanner to the periphery of the envelope of the carrier balloon 1 on aportion which urges it into circumferential tension when said carrierballoon is in proximity to the ground. It should be noted that theproduction of these two envelopes and their securing may be carried outsimultaneously by means of an apparatus such as describes in FrenchPatent Application 86.03553 in the name of the applicant. The fixing ofthe annular edge of the hot air balloon 3 to the carrier balloon 1comprises, firstly glueing or adhering said annular edge to the carrierballoon. Then, a circumferential ribbon is arranged around the annularrim and finally the ribbon is glued to the carrier balloon 1 and the hotair balloon 3.

The flattened bottom 5 of the envelope is itself produced from amaterial which is permeable to the gas in the ambient atmosphere. It maybe formed of a largely porous fabric. One embodiment which isillustrated in FIGS. 4, 5a and 5b comprises using fibers 7 of the samelength spaced one from the others and extending radially with respect tothe axis of revolution of the hot air balloon 3. The production of theflattened bottom 5 is achieved by making up several similarly formedgores 8, each of a plurality of spaced fibers 7.

The process carried out for production these gores 8 is shown in FIGS.5a and 5b. The fibers 7, of a material such as polyester or polyamide,are arranged parallel one to the others on a table.

They are fixed, at one of their extremities, to a flexible elastic band9 which held in extension on the table. At their other extremity, theyare sewn to a band 10 of a flexible fabric having elastic propertieswith respect to the polyester film forming the cylindrical portion 4.The object of this intermediate band 10 is to dampen stresses in such amanner as to not transmit to the polyester film the possibleirregularities of forces to which the fibers 7 are subjected, to avoidany risk of tearing the film.

The connection between the intermediate band 10 and the gore ofpolyester film is finally assured by a ribbon of polyethylene 11. Oncethese assemblies are achieved, the flexible elastic band 9 is released,in such a manner that each gore 8 forms a circular sector centered onthe axis of revolution of the hot air balloon 3.

Each of these gores 8 is then fixed, through the flexible elastic band7, to an annular piece 12 defining the permanent opening 6 of the hotair balloon 3.

The hot air balloon 3 also comprises an interpolar connection 13 fixedto the lower pole of the carrier balloon 1 in the extension of theinterpolar connection 2 thereof, and extends below the lower pole of thehot air balloon 3, in order to support a load 14.

This interpolar connection 13 is guided at the level of the lower poleof the hot air balloon 3, by means of an annular guide 15 centered onthe axis of revolution of this hot air balloon and secured to theannular piece 12 by means of radial fixing members 16. These fixingmembers 16 may, for example, be formed of cables of "Kevlar".

The hot air balloon 3 also includes an auxiliary strand 17 fixed at oneend to the interpolar connection 13 between the load 14 and the lowerpole of this hot air balloon, and at the other end to a guide rim 15.This auxiliary strand 17 has a length adapted to be drawn into tensionat a predetermined state of filling of the hot air balloon 3. Thepurpose of such a strand is to cause the envelope of the hot air balloon3 to undergo a longitudinal tension, by passing through the envelope apart of the load 14 carried by the space balloon. One thus avoids anyrisk of wind damage to this envelope which could destroy the latter.

The various elements constituting the aerostat and their arrangementhaving been described, the characteristics of the operation will now beexplained.

This aerostat is particularly intended to be transported by means of asatellite and then parachuted to the proximity of the planet Mars, tocarry out the exploration thereof. After the parachuting, the means forinflating the carrier balloon with a gas such a helium, lighter than thegas present in the atmosphere, will permit filling of this carrierballoon with a predetermined mass of gas. The evolution cycle of thespace balloon between the ground of the planet and a predeterminedceiling altitude is then as follows.

During the night, the temperature of the gas present in the atmosphere,and thus the gas contained in the hot air balloon 3, is relatively low.The hot air balloon 3 therefor does not produce any lift or risingforce. The aerostat then is found in proximity to the ground with theload 14 resting thereon, only under the lift of the carrier balloon 1(FIG. 1).

At day break, the slight heating of the gas present in the atmospherecauses a rapid filling of the hot air balloon 3 due to its significantresidual volume. This latter reaches its filled state and provides amaximum force for the launch and into the lower layers. Further, in thefilled state of the hot air balloon 3, the tensile forces of theauxiliary strand 17 assures against any risk of wind damage (FIG. 2). Itshould also be noted that the fact that the hot air balloon 3 has asizeable residual volume permits reducing the mass of gas contained inthe carrier balloon 1, and as a result, the weight of the inflatingmeans therefor. This latter point is very important from the perspectiveof a launching by satellite where any increase in weight is verysignificant.

In relation to the elevation of the aerostat, the volume of the carrierballoon 1 increases from the fact of reduced pressure of the atmosphere,and as a result, the volume of the hot air balloon 3 decreasesproportionally (FIG. 3). Its lifting force therefor reduces, and this isparticularly the case since the heating of the gas is less when the sunis at its zenith because of the absence of a dome.

Finally, when the sun goes down, the temperature of the gas contained inthe hot air balloon 3 decreases progressively, causing a slow descent ofthe aerostat towards the ground.

The dimensional characteristics of such an aerostat will be a functionof the type of mission planned. As a general rule, the aspect ratio ofthe carrier balloon 1 (the ratio of its height to diameter) will beequal to 2 or 3 times its variation in volume between the ground and thepredetermined ceiling altitude.

Thus, for example, for the exploration of the planet Mars, with aceiling altitude of 4 to 6 kilometers, the aspect ratio of the carrierballoon 1 will be 6 or 7, the ratio of density of the gas beingessentially 2 between this altitude and the ground.

We claim:
 1. An aerostat for travel in an autonomous and reversiblemanner between the ground of a planet having an atmosphere and apredetermined ceiling altitude, comprising:a carrier balloon (1)comprising a closed envelope defining an upper pole and a lower pole andintended to contain a gas lighter than the gas present in the ambientatmosphere, a hot air balloon (3) comprising an envelope of a materialcapable of absorbing solar radiation and emitting infrared radiation tothe interior of the hot air balloon in such a manner as to heat theenclosed gas, said envelope comprising a lower extremity having apermanent opening (6) for filling the hot air balloon (3) with the gaspresent in the ambient atmosphere, said carrier balloon (1) comprisingan envelope having a symmetry of revolution about an axis and producedfrom a material transparent to solar radiation and comprising anessentially cylindrical portion, and an upper pole and a lower polesituated on the axis of revolution, said hot air balloon (3) comprisesan envelope having a symmetry of revolution about an axis and furthercomprising an essentially cylindrical portion (4), said hot air balloon(3) having an open extremity opposite its lower extremity and defined byan annular edge of an annular cross section conjugate with that of thecarrier balloon, and a flattened bottom (5) comprising a permanentlyopening (6), gas tight fastening means securing the annular edge of thehot air balloon to the peripheral wall of the carrier balloon (1), andadapted to secure the envelopes of aid carrier balloon and said hot airballoon so that the carrier balloon (1) extends partially into theinterior of the envelope of the hot air balloon (3).
 2. An aerostat asin claim 1 wherein the hot air balloon (3) includes an annular piece(12) of a rigid material defining its permanent opening (6),characterized in that the flattened bottom (5) of said hot air balloonis made of a material permeable to the gas present in the ambientatmosphere.
 3. An aerostat as in claim 2, and wherein said flattenedbottom (5) of the hot air balloon (3) is formed of a plurality ofstrands (7) of the same length and spaced radially with respect to theaxis of revolution of said hot air balloon, said strands being fixednear one of their extremities to a strip of flexible material adapted tobe secured to the annular piece (12), and toward their oppositeextremity to an intermediate strip (10) of a material elastic withrespect to the material comprising the cylindrical portion (4), thelower extremity of said cylindrical portion being secured to saidintermediate strip (10).
 4. An aerostat as in claim 3, and wherein saidhot air balloon (3) includes:an interpolar connection (13) fixed to thelower pole of the carrier balloon (1) and extending below the lower poleof said hot air balloon for supporting a load (14), a guide rim (15) forthe interpolar connector (13) centered on the axis of revolution of saidhot air balloon at the level of its lower pole and fixed to the annularrim (12) by means of radial securing members (16).
 5. An aerostat as inclaim 4 and wherein said interpolar connection (13) of the hot airballoon (3) extends above the lower pole of the carrier balloon (1) soas to connect the latter to the upper pole of said carrier balloon. 6.An aerostat as in claim 5, and further comprising an auxiliary strand(17) fixed at one end to the interpolar connection (13) between the load14 and the lower pole of the hot air balloon (3) and at the other end tothe guide rim (15), said auxiliary strand being of a length adapted tobe placed under tension for a predetermined state of filling of the hotair balloon (3).
 7. An aerostat as in claim 1 and wherein said envelopesof the carrier balloon (1) and of the hot air balloon (3) are made ofpolyester of 3.5 microns thickness, the envelope of the hot air balloon(3) being coated internally with a metallized layer. PG,19
 8. A processfor producing an aerostat for carrying a load (14) and travelling in areversible and autonomous manner between the round of a planet having anatmosphere and a predetermined ceiling altitude comprising:providing aclosed carrier balloon envelope (1) defining a lower pole and an upperpole for enclosing a gas lighter than the gas present in the atmosphere,providing a hot air balloon having an envelope (3) of a material able toabsorb solar radiation and emit infrared radiation, and comprising alower extremity having a permanent opening (6). estimating the variationof lift per unit of volume of the hot air balloon (3) in the absence andin the presence of solar radiation and determining the volume of thishot air balloon (3) necessary to obtain the launching of the aerostatand the load, determining a mass of gas ml which is, in the absence ofsolar radiation;necessary in the carrier balloon (1) to assure thesupport of said carrier balloon (1) and the hot air balloon (3) abovethe ground, and less than the mass of gas necessary in the carrierballoon (1) to assure the launching of the aerostat and the load (14),providing said carrier balloon (1) of a material transparent to solarradiation and having a symmetry of revolution about an axis andcomprising an essentially cylindrical portion, and an upper pole and alower pole situated on the axis of revolution, said carrier balloonbeing of dimensions adapted so that its volume is essentially greaterthan the volume occupied by the mass of gas ml at the predeterminedceiling altitude, providing said hot air balloon (3) with a symmetry ofrevolution about an axis and an essentially cylindrical portionhaving:an open upper extremity defined by an annular edge of across-section conjugate with that of the carrier balloon (1), aflattened bottom (5) comprising a permanent opening (6), surrounding thehot air balloon (3) about the carrier balloon (1) at its annular edge insuch a manner that:the carrier balloon (1) extends partially into theinterior of the hot air balloon (1), the annular edge of the hot airballoon is positioned opposite a zone o the cylindrical portion of thecarrie balloon placed into circumferential tension on the ground for amass of gas ml, the residual volume of the hot air balloon (3) on theground corresponds to the volume necessary to obtain the launching ofthe aerostat and the load (14), and securing the annular rim of the hotair balloon (3) to the periphery of the envelope of the carrier balloon(1).
 9. A process for producing an aerostat as in claim 8, and whereinthe securing of the annular edge of the hot air balloon (3) to thecarrier balloon (1) comprises:adhering said annular edge to said carrierballoon, arranging a circumferential strip about the annular edge of thehot air balloon (3) and adhering this strip respectively to the carrierballoon (1) and to said hot air balloon.
 10. A process for launching anaerostat as in claim 1 carrying a load (14), and including filling thecarrier balloon (1) with a mass ml of gas lighter than the gas presentin the atmosphere said mass being, such that said balloon has:a state ofbeing full at a predetermined ceiling altitude, a state of minimuminflation on the ground for which it has a lift sufficient to maintainthe carrier balloon (1) and the hot air balloon (3) above the ground andinsufficient to bring about the launching of the aerostat and the load(14).